It is known to form membranes in the aperture of a loop or a series of loops with opening widths of 2.5-7.5 cm, or between at least two substantially parallel filaments spaced at a distance of less than 2.5 cm to define elongated apertures having lengths which greatly exceed the distance between said filaments. The resulting membranes each have a substantial surface area which is free of support material and are quite vulnerable to rupture caused by the pressure differences applied across such membranes in reverse osmosis processes.
It is further known to use woven cloth as support for membranes having a thickness substantially equal to the cloth which is twice the thickness of the yarns forming the cloth at crossover points in the cloth weave. Due to said membrane thickness the flux of a permeable compound through the membrane will be unacceptably low in many cases.
For many applications it would be desirable to have at one's disposal dense (i.e. non-porous) thin membranes (permitting high rates of flow therethrough) which possess sufficient strength to be applied in industrial separation processes.
It has now been found that excellent supported membranes can be provided by locating dense membranes in the openings of a non-woven monofilament support layer.